Grain-oriented electrical steel sheet and method for manufacturing the same

ABSTRACT

A grain oriented electrical steel sheet according to one embodiment of the present disclosure comprises: 1.0 wt % to 4.0 wt % of Si, 0.002 wt % or less (excluding 0%) of C and 0.001 wt % to 0.1 wt % of Bi, with the remainder being Fe and other unavoidable impurities.

TECHNICAL FIELD

The present disclosure relates to a grain oriented electrical steel sheet and a method for manufacturing the same.

BACKGROUND ART

The grain oriented electrical steel sheet is a soft magnetic material having superior magnetic properties in the rolling direction, which comprises crystal grains having a crystal orientation of {110}<001>, so-called Goss orientation, of the steel sheet.

Such grain oriented electrical steel sheet is manufactured by heating the slab, followed by the hot rolling, the hot-rolled sheet annealing, and the cold rolling to be rolled with a final thickness of 0.15 mm to 0.35 mm, and followed by the primary recrystallization annealing and the high-temperature annealing for forming the secondary recrystallization.

Here, it is known that at the high-temperature annealing, the slower the rate of temperature increase, the higher the degree of integration of the Goss orientation, which is secondarily recrystallized, thereby obtaining great magnetism. Typically, the rate of temperature increase during the high-temperature annealing of the grain oriented electrical steel sheet is 15° C. or less per hour. It takes 2 days to 3 days to heat up and requires 40 hours or more of purification annealing. The process may be said to consume a lot of energy. In addition, the current high-temperature annealing process is performed in the batch-type annealing with the coil state, which causes the following difficulties in the process. First, the heat treatment in the coil state causes the temperature deviation between the outer and inner of the coil, and the same heat treatment pattern cannot be applied to all parts, resulting in the magnetism deviation between the outer and inner of the coil. Second, various surface defects occur in the process of coating MgO on the surface after the decarburization-annealing and base-coating during high-temperature annealing, resulting in a decrease in the yield. Third, since the decarburization-annealed decarburized sheet is wound in the form of a coil, followed by the high-temperature annealing and the flattening annealing to perform the insulation coating, the manufacturing process is divided into three stages, which causes a problem that the yield is lowered.

DISCLOSURE Technical Problem

An exemplary embodiment of the present disclosure provides a grain oriented electrical steel sheet and a method for manufacturing the same.

Technical Solution

An exemplary embodiment of the present disclosure provides a grain oriented electrical steel sheet, comprising 1.0 wt % to 4.0 wt % of Si, 0.002 wt % or less (excluding 0%) of C and 0.001 wt % to 0.1 wt % of Bi, with the remainder being Fe and other unavoidable impurities.

Another embodiment of the present disclosure may provide the grain oriented electrical steel sheet further including 0.05 wt % or less (excluding 0%) of Mn, 0.01 wt % or less (excluding 0%) of Al, 0.001 wt % or less (excluding 0%) of S and 0.001 wt % or less (excluding 0%) of N.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet further including 0.1 wt % or less (excluding 0%) of P, 0.05 wt % or less (excluding 0%) of Mo, 0.1 wt % or less (excluding 0%) of Sn and 0.05 wt % or less (excluding 0%) of Sb.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the volume ratio of the crystal grains having a diameter of 20 μm to 500 μm may be 80% or more.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the volume ratio of the Goss crystal grains parallel in the error range of 15° or less with respect to the sheet surface of the steel sheet may be 80% or more.

Yet another exemplary embodiment of the present disclosure may provide a method of manufacturing the grain oriented electrical steel sheet, the method comprising: heating a slab comprising 1.0 wt % to 4.0 wt % of Si, 0.01 wt % to 0.4 wt % or less of C, with the remainder being Fe and other unavoidable impurities; hot-rolling the slab to produce a hot-rolled sheet; hot-rolled sheet-annealing the hot-rolled sheet; cold-rolling the hot-rolled sheet-annealed hot-rolled sheet to produce a cold-rolled sheet; decarburization-annealing the cold rolled sheet; and final-annealing the decarburization-annealed electrical steel sheet, wherein after the annealing of the hot-rolled sheet, the average diameter of the crystal grains in the surface layer of the hot-rolled sheet may be 150 to 250 μm.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the slab may further include 0.001 to 0.1 wt % of Bi.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the slab may further include 0.05 wt % or less (excluding 0%) of Mn, 0.01 wt % or less (excluding 0%) of Al, 0.001 wt % or less (excluding 0%) of S and 0.001 wt % or less (excluding 0%) of N.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the slab may further include 0.1 wt % or less (excluding 0%) of P, 0.05 wt % or less (excluding 0%) of Mo, 0.1 wt % or less (excluding 0%) of Sn and 0.05 wt % or less (excluding 0%) of Sb.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the heating temperature in the heating of the slab may be 1100° C. to 1350° C.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the hot-rolled sheet-annealing may include the decarburization process.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the hot-rolled sheet-annealing may include the first hot-rolled sheet-annealing at a temperature of 850° C. to 1000° C. and a dew-point temperature of 50° C. to 70° C. and the second hot-rolled sheet-annealing at a temperature of 1000° C. to 1200° C. and a dew-point temperature of 000° C. or less.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the first hot-rolled sheet-annealing may be performed for 10 seconds to 300 seconds, and the second hot-rolled sheet-annealing may be performed for 10 seconds to 180 seconds.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the process from the cold-rolling to the final-annealing may be continuously performed.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the process of the cold-rolling and the decarburization-annealing may be repeated at least twice.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the decarburization-annealing may be performed at a temperature of 850° C. to 1000° C. and a dew-point temperature of 50° C. to 70° C.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the final-annealing may include the first final-annealing at a temperature of 850° C. to 1000° C. and a dew-point temperature of 70° C. or less and the second final-annealing at a temperature of 1000° C. to 1200° C. under an atmosphere of H₂ 50 volume % or more.

Yet another embodiment of the present disclosure may provide the grain oriented electrical steel sheet in which the first final-annealing may be performed for 10 seconds to 180 seconds, and the second final-annealing may be performed for 10 seconds to 600 seconds

Advantageous Effects

According to an embodiment of the present disclosure, it is possible to provide the method of manufacturing the grain oriented electrical steel sheet, which is capable of performing the continuous annealing, instead of the batch-type annealing, for a coil-type product at the final-annealing.

According to another embodiment of the present disclosure, it is possible to produce a grain oriented electrical steel sheet having superior magnetic properties even with only a short time of final annealing.

According to yet another embodiment of the present disclosure, it is not necessary for winding the cold-rolled steel.

According to yet another embodiment of the present disclosure, it is possible to provide the grain oriented electrical steel sheet that does not use a grain growth inhibitor.

According to yet another embodiment of the present disclosure, it is possible to exclude nitriding-annealing, thereby stably producing the grain oriented electrical steel sheet having superior magnetic properties.

DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the results of distribution analysis of the crystal grains obtained after the hot-rolled sheet annealing of the hot rolled sheet including 500 ppm of Bi in Example 2.

FIG. 2 illustrates the results of distribution analysis of the crystal grains obtained after the hot-rolled sheet annealing of the hot rolled sheet without Bi in Example 2.

MODE FOR INVENTION

The terms “first,” “second,” “third” and the like are used to illustrate different parts, components, areas, layers and/or sections, but are not limited thereto. The terms are only used to differentiate a certain part, component, area, layer or section from other part, component, area, layer or section. Accordingly, a first part, component, area, layer or section, which will be mentioned hereinafter, may be referred to as a second part, component, area, layer or section without departing from the scope of the present disclosure.

The technical terms used herein are set forth to mention specific embodiments of the present disclosure and do not intend to define the scope of the present disclosure. The singular number used here includes the plural number as long as the meaning of the singular number is not distinctly opposite to that of the plural number. The term “have,” used herein refers to the concretization of a specific characteristic, region, integer, step, operation, element and/or component, but does not exclude the presence or addition of other characteristic, region, integer, step, operation, element and/or component.

When it is said that any part is positioned “on” or “above” another part, it means the part is directly on the other part or above the other part with at least one intermediate part. In contrast, if any part is said to be positioned “directly on” another part, it means that there is no intermediate part between the two parts.

Unless otherwise specified, all the terms including technical terms and scientific terms used herein have the same meanings commonly understandable to those skilled in the art relating to the present disclosure. The terms defined in generally used dictionaries are additionally interpreted to have meanings corresponding to relating scientific literature and contents disclosed now, and are not interpreted either ideally or very formally unless defined otherwise.

Unless otherwise described, % means weight %, and 1 ppm is 0.0001 wt %.

Hereinafter, exemplary embodiments of the present disclosure will be described in detail so that a person having ordinary knowledge in the art to which the present disclosure belongs can easily carry out the present disclosure. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

In the conventional technology for grain oriented electrical steel sheets, precipitates such as AlN and MnS were used as crystal grain growth inhibitors. All processes strictly controlled the distribution of precipitates, and there were conditions for removing precipitates remaining in the secondary recrystallized steel sheet. Thus, process conditions were severely constrained.

On the other hand, in one embodiment of the present disclosure, precipitates such as AlN and MnS are not used as the grain growth inhibitor, and secondary recrystallization is not used. In an embodiment of the present disclosure, Bi is used to effectively grow the crystal grain of the surface layer at the hot-rolled sheet-annealing, thereby increasing the ratio of Goss grain to obtain an electrical steel sheet having superior magnetic properties.

The grain oriented electrical steel sheet of an exemplary embodiment of the present disclosure comprises 1.0 wt % to 4.0 wt % of Si, 0.002 wt % or less (excluding 0%) of C and 0.001 wt % to 0.1 wt % of Bi, with the remainder being Fe and other unavoidable impurities.

Hereinafter, each component is described in detail.

Silicon (Si) lowers the magnetic anisotropy of the electrical steel sheet and increases the resistivity to improve the iron loss. When the Si content is less than 1.0 wt %, the iron loss is inferior. When the Si content exceeds 4.0 wt %, the brittleness is increased. Therefore, the Si content in the slab and in the grain oriented electrical steel sheet after the final annealing may be 1.0 wt % to 4.0 wt %.

The carbon (C) content may be 0.01 wt % to 0.4 wt % in the slab because the C in the center part comes out to the surface layer in order to diffuse the Goss crystal grain in the surface layer to the center part during the hot-rolled sheet-annealing, the cold-rolled sheet-decarburization annealing and final annealing. Further, the C content may be 0.0020 wt % or less in the grain oriented electrical steel sheet after the final annealing in which the decarburization is completed.

Bismuth (Bi) is a segregation element with high volatility. When it is positioned in the surface layer, Bi is volatilized on the surface, resulting in the crystal grain coarsening in the surface layer. On the other hand, Bi is located in the center of the steel, thereby having effects of refining crystal grains. If the Bi content is less than 0.001 wt %, the effect may be insignificant. On the contrary, when it is added in an amount exceeding 0.1 wt %, Bi causes nonuniformity in the size of the surface crystal grain, so it is preferably added in an amount of 0.001 wt % to 0.1 wt %.

In an exemplary embodiment of the present disclosure, since precipitates such as AlN and MnS are not used as a crystal growth inhibitor, elements essentially used in general oriented electrical steel sheets such as manganese (Mn), aluminum (Al), nitrogen (N) and sulfur (S) are managed in a range as impurities. In other words, when it further includes Mn, Al, N, S or the like inevitably, the steel sheet may further include 0.05 wt % or less of Mn, 0.01 wt % or less of Al, 0.001 wt % or less of S and 0.001 wt % or less of N. More specifically, Al may be included in an amount of 0.005 wt % or less.

Further, the steel sheet may further include 0.1 wt % or less (excluding 0%) of P, 0.05 wt % or less (excluding 0%) of Mo, 0.1 wt % or less (excluding 0%) of Sn and 0.05 wt % or less (excluding 0%) of Sb.

Phosphorus (P) is an element which promotes the formation of Goss crystal grains. When it is added too much, P may cause cracks and interfere with the grain growth. Specifically, P may be included in an amount of 0.001 wt % to 0.1 wt %.

Molybdenum (Mo) is an element which promotes the formation of Goss grain of the hot-rolled sheet

Mo does not interfere with the decarburization, but when it is added excessively, the crystal grain imbalance may occur. Specifically, Mo may be included in an amount of 0.001 wt % to 0.05 wt %.

Tin (Sn) is an element which promotes the formation of Goss crystal grains. When it is added too much, Sn may be segregated in the surface to interfere with the decarburization, thereby inhibiting the crystal growth. Specifically, Sn may be included in an amount of 0.001 wt % to 0.1 wt %.

Antimony (Sb) is an element which promotes the formation of Goss crystal grains. When it is added too much, Sb may be segregated in the surface to interfere with the decarburization, thereby inhibiting the crystal growth. Specifically, Sb may be included in an amount of 0.001 wt % to 0.05 wt %.

In addition, as other unavoidable impurities, components such as Ti, Mg, and Ca react with oxygen to form oxides in the steel, which may interfere with the magnetic migration of the final product as an inclusion to cause magnetic deterioration. Thus, it is necessary to suppress impurities strictly. Accordingly, when they are inevitably included, the impurities may be controlled in an amount of 0.005 wt % or less for each component.

In the grain oriented electrical steel sheet, the volume ratio of the crystal grains having a diameter of 20 μm to 500 μm may be 80% or more. When the volume ratio of the crystal grains having a diameter of 20 μm to 500 μm is less than 80%, the crystal grains may not grow sufficiently, thereby deteriorating the magnetism.

The volume ratio of the Goss crystal grains parallel in the error range of 15° or less with respect to the sheet surface of the steel sheet may be 80% or more. When the volume ratio of the Goss crystal grains is less than 80%, sufficient magnetism may not be secured.

The method of manufacturing the grain oriented electrical steel sheet of an exemplary embodiment of the present disclosure comprises heating a slab comprising 1.0 wt % to 4.0 wt % of Si, 0.01 wt % to 0.4 wt % of C, with the remainder being Fe and other unavoidable impurities; hot-rolling the slab to produce a hot-rolled sheet; hot-rolled sheet-annealing the hot-rolled sheet; cold-rolling the hot-rolled sheet-annealed hot-rolled sheet to produce a cold-rolled sheet; decarburization-annealing the cold rolled sheet; and final-annealing the decarburization-annealed electrical steel sheet.

Hereinafter, the method of manufacturing the grain oriented electrical steel sheet is described in detail for each step.

First, the slab is heated.

Since the composition of the slab has been described specifically with respect to the composition of the electrical steel sheet, the duplicate description is excluded.

The temperature of heating the slab may be 1100° C. to 1350° C. higher than the normal heating temperature. When the temperature of heating the slab is high, the hot-rolled structure is coarsened to have a problem of affecting magnetism adversely. However, in the method of manufacturing the grain oriented electrical steel sheet of an exemplary embodiment of the present disclosure, since the content of carbon in the slab is higher than that in the conventional slab, the hot-rolled structure is not coarsened even when the temperature of heating the slab is high. Further, the slab is heated at a temperature higher than the normal heating temperature, so that it is advantageous in the hot-rolling.

Next, the slab is hot-rolled to produce the hot-rolled sheet. The hot-rolling temperature is not limited, but the hot-rolling may be finished at 950° C. or less in an exemplary embodiment.

Next, the hot-rolled sheet is annealed. In this step, the hot-rolled sheet-annealing may include the decarburization process. Specifically, the decarburization annealing can be carried out at a dew point temperature of 50° C. to 70° C. in an austenite single phase region or ferrite and austenite composite phase region. In this step, the temperature may have a range of 850° C. to 1000° C.

Further, the atmosphere may be a mixed gas atmosphere of hydrogen and nitrogen. Further, the decarbonization amount in the decarburization annealing may be 0.0300 to wt % 0.0600 wt %. More specifically, in order to include the decarburization process, the hot-rolled sheet-annealing may include the first hot-rolled sheet-annealing at a temperature of 850° C. to 1000° C. and a dew-point temperature of 50° C. to 70° C. and the second hot-rolled sheet-annealing at a temperature of 1000° C. to 1200° C. and a dew-point temperature of 0° C. or less. More specifically, the first hot-rolled sheet-annealing may be performed for 10 seconds to 300 seconds, and the second hot-rolled sheet-annealing may be performed for 10 seconds to 180 seconds.

In the decarburization-annealing process, the crystal grain size on the surface of the hot-rolled sheet grows to be coarse, but the crystal grains inside the electrical steel sheet remain as a fine structure. After the decarburization-annealing, the ferrite crystal grain size of the surface portion may be 150 μm to 250 μm. At this time, the size of the average diameter of crystal grains in the surface layer is controlled by the range as described above, thereby increasing the ratio of the Goss grain of the finally produced grain oriented electrical steel sheet and improving the magnetic property of the grain oriented electrical steel sheet.

Next, after the hot-rolled sheet-annealing, the hot-rolled sheet is cold-rolled to produce the cold-rolled sheet. In the conventional manufacturing process of the grain oriented electrical steel sheet having high magnetic flux density, it is known that it is effective to perform the cold rolling one time at a high reduction ratio close to 90%. This is because only the Goss crystal grains among the first recrystallized grains are favorable for grain growth.

However, the method of manufacturing the grain oriented electrical steel sheet of an exemplary embodiment of the present disclosure does not use the abnormal grain growth of Goss orientation grains but internally diffuses the Goss grains of the surface layer generated by the decarburization-annealing and the cold rolling. Thus, it is advantageous to form them so as to distribute a plurality of Goss orientation crystal grains in the surface layer.

Therefore, when the cold rolling is performed at a reduction ratio of 50% to 70%, a plurality of Goss textures may be formed in the surface layer. Further, it may be 55% to 65%.

Next, the cold-rolled sheet is decarburization-annealed. The decarburization-annealing may be performed at a temperature of 850 to 1000° C. and a dew-point temperature of 50 to 70° C.

Further, when the process of the cold-rolling and the decarburization-annealing is carried out at least two times, a plurality of Goss textures may be formed in the surface layer.

Next, after the decarburization-annealing, the electrical steel sheet is final-annealed.

In the method of manufacturing the grain oriented electrical steel sheet of an exemplary embodiment of the present disclosure, the final-annealing is performed continuously after the cold-rolling, unlike the conventional batch-type. In other words, the process from the cold-rolling to the final-annealing may be continuously performed. Therefore, it is not necessary to apply the annealing separator.

The final-annealing may include the first final-annealing at a temperature of 850° C. to 1000° C. and a dew-point temperature of 70° C. or less and the second final-annealing at a temperature of 1000° C. to 1200° C. under an atmosphere of H₂ 50 volume % or more. More specifically, the second final-annealing may be performed under an atmosphere of H₂ 90 volume % or more.

As described above, in an exemplary embodiment of the present disclosure, the Bi segregation may be used as a grain growth inhibitor, but the AlN precipitate is not used. Therefore, the burden of the purification-annealing for decomposing and removing AlN and MnS is reduced.

Hereinafter, the present disclosure is described in detail with reference to Examples. However, these Examples are only illustrative for the present disclosure, and the present disclosure is not limited by Examples.

Example 1

The slab comprising 3.23 wt % of Si and 0.25 wt % of C, with the remainder being Fe and other unavoidable impurities was heated at a temperature of 1250° C., followed by the hot-rolling to produce the hot-rolled sheet with a thickness of 1.6 mm. Then, the annealing was performed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 120 seconds. Then, the hot-rolled sheet-annealing was performed at an annealing temperature of 1100° C. and at a dew point temperature of 0° C. or less in an atmosphere of hydrogen and nitrogen mixed gas for a period of time listed in Table 1 below. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%.

The cold-rolled sheet was again annealed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 60 seconds. Then, the decarburization-annealing was performed at an annealing temperature of 1100° C. in an atmosphere of hydrogen and nitrogen mixed gas at a dew point temperature of 0° C. for 50 seconds. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%.

Thereafter, while the final-annealing, the decarburization-annealing was performed at a temperature of 900° C. in a moisture atmosphere of hydrogen and nitrogen mixed gas (i.e., dew-point temperature of 60° C.) for 60 seconds. Then, the heat treatment was performed under an atmosphere of H₂ 100 volume % at 1050° C. for 3 minutes. The annealing time at 1100° C. during the hot-rolled sheet-annealing, the diameter of the crystal grains of the surface layer after the hot-rolled sheet-annealing, the ratio of the Goss grains of the final electrical steel sheet, and the magnetic properties of the final electrical steel sheet were measured in the following Table 1.

TABLE 1 Diameter of crystal Goss Annealing grain in crystal time surface layer ratio B10 W17/50 (seconds) (μm) (%) (tesla) (W/kg) Classification 0 89 55 1.68 2.58 Comparative material 55 158 80 1.83 1.19 Inventive material 78 175 84 1.85 1.10 Inventive material 95 182 87 1.87 1.06 Inventive material 120 195 89 1.90 0.99 Inventive material 150 205 88 1.90 0.99 Inventive material

As listed in Table 1, it can be found that as the annealing time at the dew point temperature of 0° C. or less and the annealing temperature of 1100° C. is longer, the grains of the surface layer grow to elicit the superior Goss ratio and magnetic properties. However, if the annealing time becomes longer than the proper value, the crystal grains inside them grow so that the structure becomes uneven during the decarburization-annealing after the cold-rolling, thereby deteriorating the final magnetism.

Example 2

The slab comprising 3.22 wt % of Si, 0.245 wt % of C and Bi in a content listed in Table 2 below, with the remainder being Fe and other unavoidable impurities was heated at a temperature of 1250° C., followed by the hot-rolling to produce the hot-rolled sheet with a thickness of 1.6 mm. Then, the annealing was performed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 120 seconds. Then, the hot-rolled sheet-annealing was performed at an annealing temperature of 1100° C. and at a dew point temperature of 0° C. or less in an atmosphere of hydrogen and nitrogen mixed gas for 30 seconds. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%.

The cold-rolled sheet was again decarburization-annealed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 60 seconds. Then, the annealing was performed at an annealing temperature of 1100° C. in an atmosphere of hydrogen and nitrogen mixed gas at a dew point temperature of 0° C. for 50 seconds. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%.

Thereafter, while the final-annealing, the decarburization-annealing was performed at a temperature of 900° C. in a moisture atmosphere of hydrogen and nitrogen mixed gas (i.e., dew-point temperature of 60° C.) for 60 seconds. Then, the heat treatment was performed under an atmosphere of H₂ 100 volume % at 1050° C. for 3 minutes. The Bi content at the hot-rolled sheet-annealing, the diameter of the crystal grains of the surface layer after the hot-rolled sheet-annealing, the ratio of the Goss grains of the final electrical steel sheet, and the magnetic properties of the final electrical steel sheet were measured in the following Table 2.

TABLE 2 Diameter of crystal Goss Bi grain in crystal Content surface layer ratio B10 W17/50 (wt %) (μm) (%) (tesla) (W/kg) Classification 0 115 65 1.69 2.21 Comparative material 0.02 151 81 1.85 1.15 Inventive material 0.05 159 83 1.86 1.12 Inventive material 0.074 170 88 1.88 1.05 Inventive material 0.1 183 88 1.89 0.98 Inventive material 0.15 195 76 1.79 1.69 Comparative material

Table

As listed in Table 2, it can be found that the Bi is used as a grain growth inhibitor, thereby appropriately adjust the grain diameter of the surface layer after the hot-rolled sheet-annealing and having the superior Goss ratio and magnetic properties.

Example 3

The slab comprising 3.19 wt % of Si, 0.24 wt % of C and 0.05 wt % of Bi, with the remainder being Fe and other unavoidable impurities was heated at a temperature of 1250° C., followed by the hot-rolling to produce the hot-rolled sheet with a thickness of 1.6 mm. Then, the annealing was performed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 120 seconds. Then, the hot-rolled sheet-annealing was performed at an annealing temperature of 1100° C. and at a dew point temperature of 0° C. or less in an atmosphere of hydrogen and nitrogen mixed gas for a period of time listed in Table 3 below. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%.

The cold-rolled sheet was again decarburization-annealed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 60 seconds. Then, the annealing was performed at an annealing temperature of 1100° C. in an atmosphere of hydrogen and nitrogen mixed gas at a dew point temperature of 0° C. for 50 seconds. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%.

Thereafter, while the final-annealing, the decarburization-annealing was performed at a temperature of 900° C. in a moisture atmosphere of hydrogen and nitrogen mixed gas (i.e., dew-point temperature of 60° C.) for 60 seconds. Then, the heat treatment was performed under an atmosphere of H₂ 100 volume % at 1050° C. for 3 minutes. The annealing time at 1100° C. during the hot-rolled sheet-annealing, the diameter of the crystal grains of the surface layer after the hot-rolled sheet-annealing, the ratio of the Goss grains of the final electrical steel sheet, and the magnetic properties of the final electrical steel sheet were measured in the following Table 3.

TABLE 3 Diameter of crystal Goss Annealing grain in crystal time surface layer ratio B10 W17/50 ( 

 ) (μm) (%) (tesla) (W/kg) Classification 0 95 60 1.68 2.22 Comparative material 30 459 81 1.82 1.18 Inventive material 75 211 82 1.83 1.15 Inventive material 90 223 87 1.88 1.02 Inventive material 110 229 90 1.91 0.97 Inventive material 145 240 92 1.91 0.96 Inventive material 185 262 75 1.70 1.74 Comparative material

As listed in Table 3, it can be found that as the annealing time at the dew point temperature of 0° C. or less and the annealing temperature of 1100° C. is longer, the grains of the surface layer grow to elicit the superior Goss ratio and magnetic properties. However, if the annealing time becomes longer than the proper value, the crystal grains inside them grow so that the structure becomes uneven during the decarburization-annealing after the cold-rolling, thereby deteriorating the final magnetism.

Example 4

The slab comprising 3.19 wt % of Si, 0.24 wt % of C and 0.05 wt % of Bi, and P, Sn, Sb, Mo, Al and Mn in the content listed in Table 4 below, with remainder being Fe and other unavoidable impurities was heated at a temperature of 1250° C., followed by the hot-rolling to produce the hot-rolled sheet with a thickness of 1.6 mm. Then, the annealing was performed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 120 seconds. Then, the hot-rolled sheet-annealing was performed at an annealing temperature of 1100° C. and at a dew point temperature of 0° C. or less in an atmosphere of hydrogen and nitrogen mixed gas for 120 seconds. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%. The cold-rolled sheet was again decarburization-annealed at an annealing temperature of 870° C. and at a dew-point temperature of 60° C. for 60 seconds. Then, the annealing was performed at an annealing temperature of 1100° C. in an atmosphere of hydrogen and nitrogen mixed gas at a dew point temperature of 0° C. for 50 seconds. Thereafter, the cooling was performed, the pickling was performed, and then the cold-rolling was performed at a reduction ratio of 60%. Thereafter, in the final-annealing, the decarburization-annealing was performed at a temperature of 900° C. in a moisture atmosphere of hydrogen and nitrogen mixed gas (i.e., dew-point temperature of 60° C.) for 60 seconds. Then, the heat treatment was performed under an atmosphere of H2 100 volume % at 1100° C. for 3 minutes. The surface crystal grain size of the hot-rolled annealed sheet according to each component, the ratio of the Goss grains of the final electrical steel sheet, and the magnetic properties of the final electrical steel sheet were measured in the following Table 5.

TABLE 4 Sn Mo Mn P (wt Sb (wt Al (wt Steel type (wt %) %) (wt %) %) (wt %) %) Inventive steel 1 0.03 0.03 0.015 0.02 0.003 0.03 Inventive steel 2 0.1 0.03 0.015 0.02 0.003 0.03 Inventive steel 3 0.03 0.07 0.015 0.02 0.003 0.03 Inventive steel 4 0.03 0.03 0.03 0.02 0.003 0.03 Inventive steel 5 0.03 0.03 0.015 0.05 0.003 0.03 Inventive steel 6 0.03 0.03 0.015 0.02 0.005 0.03 Inventive steel 7 0.03 0.03 0.015 0.02 0.003 0.05 Comparative steel1 0.2 0.03 0.015 0.02 0.003 0.03 Comparative steel 2 0.03 0.1 0.015 0.02 0.003 0.03 Comparative steel 3 0.03 0.03 0.05 0.02 0.003 0.03 Comparative steel 4 0.03 0.03 0.015 0.1 0.003 0.03 Comparative steel 5 0.03 0.03 0.015 0.02 0.01 0.03 Comparative steel 6 0.03 0.03 0.015 0.02 0.003 0.1

TABLE 5 Diameter of crystal Goss grain in crystal surface layer ratio B₁₀ W_(17/50) Steel type (μm) (%) (tesla) (W/kg) Inventive 198 92 1.91 0.98 steel 1 Inventive 187 91 1.9 0.99 steel 2 Inventive 167 93 1.92 1 steel 3 Inventive 156 91 1.91 0.98 steel 4 Inventive 199 90 1.92 0.97 steel 5 Inventive 210 89 1.89 1.01 steel 6 Inventive 177 89 1.89 1.01 steel 7 Comparative 115 77 1.81 1.23 steel 1 Comparative 122 78 1.8 1.31 steel 2 Comparative 98 71 1.75 1.51 steel 3 Comparative 133 71 1.77 1.41 steel 4 Comparative 188 60 1.69 1.77 steel 5 Comparative 154 82 1.84 1.15 steel 6

As listed in Tables 4 and 5, it can be found that the components such as P, Sn, Sb and Mo are included in an appropriate range, thereby having the effect of improving the magnetism. It can be confirmed that Al and Mn have a high degree of oxidation so that when they are included in a significant amount, crystal grains having an orientation harmful to the magnetism are formed to affect the magnetic properties adversely.

It will be understood by those skilled in the art that the present disclosure is not limited by the exemplary embodiments but can be performed in various different forms, and the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics of the present disclosure. Therefore, it is to be understood that the exemplary embodiments as described above are illustrative in all aspects and not restrictive. 

1. A grain oriented electrical steel sheet comprising: 1.0 wt % to 4.0 wt % of Si, 0.002 wt % or less (excluding 0%) of C and 0.001 wt % to 0.1 wt % of Bi, with the remainder being Fe and other unavoidable impurities.
 2. The grain oriented electrical steel sheet of claim 1, further including 0.05 wt % or less (excluding 0%) of Mn, 0.01 wt % or less (excluding 0%) of Al, 0.001 wt % or less (excluding 0%) of S and 0.001 wt % or less (excluding 0%) of N.
 3. The grain oriented electrical steel sheet of claim 1, further including 0.1 wt % or less (excluding 0%) of P, 0.05 wt % or less (excluding 0%) of Mo, 0.1 wt % or less (excluding 0%) of Sn and 0.05 wt % or less (excluding 0%) of Sb.
 4. The grain oriented electrical steel sheet of claim 1, wherein: the volume ratio of the crystal grains having a diameter of 20 μm to 500 μm is 80% or more.
 5. The grain oriented electrical steel sheet of claim 1, wherein: the volume ratio of the Goss crystal grains parallel in the error range of 15° or less with respect to the sheet surface of the steel sheet is 80% or more.
 6. A method of manufacturing a grain oriented electrical steel sheet, the method comprising: heating a slab comprising 1.0 to 4.0 wt % of Si, 0.01 wt % to 0.4 wt % of C, with the remainder being Fe and other unavoidable impurities; hot-rolling the slab to produce a hot-rolled sheet; hot-rolled sheet-annealing the hot-rolled sheet; cold-rolling the hot-rolled sheet-annealed hot-rolled sheet to produce a cold-rolled sheet; decarburization-annealing the cold-rolled sheet; and final-annealing the decarburization-annealed electrical steel sheet, wherein after the annealing of the hot-rolled sheet, the average diameter of the crystal grain in the surface layer of the hot-rolled sheet is 150 μm to 250 μm.
 7. The method of claim 6, wherein the slab further includes 0.001 wt % to 0.1 wt % of Bi.
 8. The method of claim 6, wherein the slab further includes 0.05 wt % or less (excluding 0%) of Mn, 0.01 wt % or less (excluding 0%) of Al, 0.001 wt % or less (excluding 0%) of S and 0.001 wt % or less (excluding 0%) of N.
 9. The method of claim 6, wherein: the slab further includes 0.1 wt % or less (excluding 0%) of P, 0.05 wt % or less (excluding 0%) of Mo, 0.1 wt % or less (excluding 0%) of Sn and 0.05 wt % or less (excluding 0%) of Sb.
 10. The method of claim 6, wherein: the heating temperature in the heating of the slab is 1100 to 1350° C.
 11. The method of claim 6, wherein: the hot-rolled sheet-annealing includes the decarburization process.
 12. The method of claim 6, wherein: the hot-rolled sheet-annealing includes a first hot-rolled sheet-annealing at a temperature of 850 to 1000° C. and a dew-point temperature of 50 to 70° C. and a second hot-rolled sheet-annealing at a temperature of 1000 to 1200° C. and a dew-point temperature of 0° C. or less.
 13. The method of claim 12, wherein: the first hot-rolled sheet-annealing is performed for 10 to 300 seconds, and the second hot-rolled sheet-annealing is performed for 10 to 180 seconds.
 14. The method of claim 6, wherein: the process from the cold-rolling to the final-annealing is continuously performed.
 15. The method of claim 6, wherein: the process of the cold-rolling and the decarburization-annealing is repeated at least twice.
 16. The method of claim 6, wherein: the decarburization-annealing is performed at a temperature of 850 to 1000° C. and a dew-point temperature of 50 to 70° C.
 17. The method of claim 12, wherein: the final-annealing includes a first final-annealing at a temperature of 850 to 1000° C. and a dew-point temperature of 70° C. or less and a second final-annealing at a temperature of 1000 to 1200° C. under an atmosphere of H₂ 50 volume % or more.
 18. The method of claim 17, wherein: the first final-annealing is performed for 10 to 180 seconds and the second final-annealing is performed for 10 to 600 seconds. 